Control of chemical mass shifts in the quadrupole ion trap through selection of resonance ejection working point and rf scan direction

Compound-dependent chemical mass shifts are observed and their origin is elucidated in a modified Finnigan GCQ quadrupole ion trap mass spectrometer. The dependence of chemical mass shifts on ion trap geometry, specifically the center to end-cap spacing, z0, and the size of the apertures in the end caps, is demonstrated. The effects of the working point (qeject value) used for resonance ejection and the direction of the rf mass analysis scan are also studied, and the results are found to be in agreement with a previously proposed model for the chemical mass shift mechanism. It is shown that chemical mass shifts are present when resonance ejection is used, unless the qeject is chosen to correspond to a nonlinear resonance point, where the shifts are removed. The shifts are also removed by performing the mass analysis scan in the reverse direction, i.e., from high mass to low mass.

Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.

Encounter with New Resources Causes Polarized Growth of the Cord-Forming Basidiomycete Phanerochaete velutina on Soil.

Abstract The development and physiology of cord-forming saprotrophic basidiomycetes, which form extensive and persistent mycelial networks in woodland ecosystems, can be conveniently studied on non-sterile soil in laboratory microcosms mimicking field conditions. Morphological responses of Phanerochaete velutina mycelial systems to resource encounters, and decay partitioning following encounters, varied according to whether simulated woody litter was unsterile or autoclaved and on whether encounter took place at the mycelial foraging front or behind the margin (simulating litter fall onto established systems in the field). Results show that encounter of discrete resources by P. velutina is rapidly communicated to the entire mycelial system; that resource capture takes high priority at the expense of continued system extension and decay-derived carbon reallocation; and that polarized growth toward newly encountered resources, previously considered to occur infrequently with this species, may be readily detected using image analysis techniques. Potential advantages of polarized development of P. velutina are discussed.